Configure cameras with 2 different settings?

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Paul
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Configure cameras with 2 different settings?

Post by Paul » Thu Aug 22, 2019 5:56 pm

I was wondering if it's possible to configure the cameras with different settings.

Taking night-time or low light photos works great. But when there's a full moon, the moon itself is overexposed while the landscape and the rest of the sky are fine.

So what I would like to do is configure one camera for low-light photography and the other camera for regular daytime photography.

What I'm hoping will happen is one camera will be just like I described above (the moon overexposed but everything else is fine) and the other camera with the moon showing up clearly and the rest of the picture being black as night.

Let me know if it's possible to do this. Or at least let me know if there's a way to configure the settings so that the moon doesn't get overexposed.

Thanks.

stereomaton
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Re: Configure cameras with 2 different settings?

Post by stereomaton » Thu Aug 22, 2019 9:29 pm

This effect is due to the wide dynamic range of the scene and is not related to stereo. Using the cameras independently is a good intuition, however...

With the scene you describe, there are more than 17EV (I say it roughly by estimation, it is probably a bit more), which means that the moon is approximately more than 2^17 > 128000 times brighter than the landscape.
This is way more than the approx 15EV the best sensors (at least on public cameras) of the market are capable of today (and actually it is even less in low light), and they are not at the price of the pi cameras.

To get the full range, the technique is usually to take several photos with different exposure to cover the whole range, and than merge them together in a highly controlled manner. It is known as HDR. The tonemapping might be tricky because image files and displays also have limited ranges of brightness.

The pitfall is that you would need more than 2 photos to get enough range to have enough interesting data to work with. Especially, there is a hallow around the moon due to the squatting of the atmosphere that is reduced by our brain but that the cameras see well and you would need this intermediate light values detailed enough to have interesting fused image.
I did not found the dynamic range of the pi camera sensors yet to estimate an approximative number of photos that would be a minimum. However, I think of a 3D HDR photo with probably similar dynamic in a crypt and 7 shots (per chip for the stereo) was almost too few with pretty good sensor and optics (most parts were well exposed, but there were still saturated dark and bright spots).

Usually, we take several photos in a row at high speed (hoping that nothing moves too fast ; but it can be quite slow if anything moves much) by varying the exposure between each shot instead of having several cameras. It is known as bracketing.

Using two cameras would also introduce different points of view which would make the fuse pretty bad if there exist objects near you (the more close, the worst it is) even if with so small cameras you can stick them sufficiently close together so that it is not a problem after a meter or so from the cameras.

After all this practical considerations, I can answer the original question: yes you can pilot the cameras independently by using the right parameters to control only one camera at the time in raspistill for example (you can select which camera, and control only one camera if you do not select a stereo mode).
I have not my stereopi right now to check, but with the way I understand it, you should very likely be able to control them independently this way at the same time.
But for your application, you would have better results with classical bracketing of exposure to create HDR images.
Stereophotographer and hacker
Despite my quite active participation in the forum, I am not in the StereoPi team
StereoPi Standard Edition + CM3Lite module

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Realizator
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Re: Configure cameras with 2 different settings?

Post by Realizator » Fri Aug 23, 2019 6:37 am

Paul, Stereomaton gives you perfect answer. I just like to add one notice: when you use cameras in -3d mode, their settings are synchronized by Raspbian. I mean classic raspistill implementation like this:

Code: Select all

raspistill -3d -sbs -[settings here] -o stereoimage.jpg
For your case you can use two independent issues or raspistill with unique setting for each camera, like this

Code: Select all

raspistill -cs 0 -[settings for the first camera] -o 1stcam.jpg
raspistill -cs 1 -[settings for the second camera] -o 2ndcam.jpg
Eugene a.k.a. Realizator

stereomaton
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Location: France

Re: Configure cameras with 2 different settings?

Post by stereomaton » Fri Aug 23, 2019 7:24 am

I found that the V1 and V2 cameras seem to capture about 10-11EV in bright light conditions, which is better than I would have thought, but those numbers might drop quite a lot in low light (ie when ISO are higher).
While the numbers might sound like it would be ok with 2 or 3 photos, don't forget that it is exponential. You want intermediate values to be able to produce better results.

I would advise to expose for landscape, than halve the exposure time while keeping other settings the same (which lowers by 1EV the exposure; a combination of time and ISO would be probably better but harder to explain) until the moon is underexposed. Then go to your computer with all the images to create your HDR.
Beware that because of the rotation in the Earth, the moon moves quite fast in the sky. You do not have to hurry, but don't be too slow.

The image I talked about is this one: http://phereo.com/image/5c08717ce7e564de30000199
Stereophotographer and hacker
Despite my quite active participation in the forum, I am not in the StereoPi team
StereoPi Standard Edition + CM3Lite module

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